A conventional apparatus for obtaining a tomographic image by using ultrasonic waves in the form of general elastic waves has a transmission part for transmitting ultrasonic waves in the form of elastic waves to a sample, a reception part for receiving reflected waves, and a scanning unit for scanning the transmission and reception waves. Further, provision is made for a unit for converting and visualizing a received reflected signal into a luminance signal. Thus, the interior of the sample is observed by using the time series tomographic images obtained by the above-mentioned units. In addition, in one form of the above-mentioned apparatus, a three-dimensional image is obtained by scanning an ultrasonic wave in the up and down directions as well as in the right and left directions by means of the above-mentioned scanning unit.
Now, a living body is taken as one of objects to be observed by ultrasonic waves. Ultrasonic waves have real time, handiness, non-invasiveness, and so on, which become advantages, and hence ultrasonic waves are often used to observe the interior of a living body.
Ultrasonic waves used to observe the interior of a living body are transmitted and received by a plurality of electromechanical transducers (mainly piezoelectric elements).
At the time of transmission, ultrasonic waves converging into a focal position are generated by providing electric signals to a plurality of elements in a time shifted manner so that the phases of the ultrasonic waves coincide with each other at the focal position. A region through which the ultrasonic waves generated by such driving pass is a region around a straight line connecting between the center of the plurality of elements thus driven and the focal position, and this may be sometimes called a transmission beam. Upon reception of reflected waves, the reflected signals of the ultrasonic waves at the focal position are acquired by correcting their time delays corresponding to the focal position so as to add them to the electric signals, respectively, which have been generated from the received ultrasonic waves by means of the plurality of elements. The reflected signals thus added by the electric signals from the plurality of elements become received waveform data holding the waveforms of the ultrasonic waves. Then, the received waveform data is converted into intensity data by acquiring an envelope of this received waveform data (also referred to as envelope detection). An image is finally formed by thinning or rounding this intensity data according to the pixels of the image to be displayed, and further interpolating the thus thinned or rounded intensity data as required. Here, note that the focal position at the time of the reception can be caused to change in real time. In addition, a region of the focal position generated by the reception processing of the aforementioned transmission beam may be called a received beam.
By performing such transmission and reception control, it becomes possible for the ultrasonic apparatus to image the interior of the living body by transmitting ultrasonic waves to a part to be observed, and receiving waves reflected therefrom. Here, note that a linear region acquired by these transmission beam and received beam is called a scan line, and an image is formed by arranging a plurality of pieces of data each for such a scan line in parallel to one another.
Since ultrasonic waves are able to image the interior of a living body in a non-invasive manner according to the above-mentioned principles, they are widely used for detecting various forms of the interior of the living body. Among such various forms, there is the detection of a high reflector such as a calculus. One of detection methods for a calculus which have been frequently carried out in the field of medical care is a technique that detects a calculus depending on whether an acoustic shadow is generated in an image at a rear side of the calculus, i.e., at a side far from a search unit or probe or at a deeper region. Here, note that the acoustic shadow is a shadow portion in which an image behind a high reflector is not formed because ultrasonic pulses do not reach behind the high reflector and receiving beams are interrupted by the high reflector.
In Japanese patent application laid-open No. 2003-339696, there is disclosed an ultrasonic apparatus that acquires the correlation of adjacent scan lines so as to set the density of the scan lines, and controls, as a result thereof, a transmission beam former or a reception beam former. Also, in Japanese patent application laid-open No. 2005-169155, there is disclosed an ultrasonic apparatus that extracts the outline of a tissue based on image data.
In addition, in Japanese patent application laid-open No. H04-317641, there is disclosed an ultrasonic imaging apparatus that detects a linear boundary in a tomographic image or a boundary surface in three-dimensional information by the use of the phase information of reflected waves. As a specific means, there is disclosed one that calculates, from a designated position, times at which the cross-correlation functions of the individual scan lines become maximized, and positions obtained from those times are connected to one another so that outline or contour information in a sample to be examined and a continuous boundary of an object are displayed.